1. Field of the Invention
This invention relates to methods and apparatus used in the design and manufacture of surfboards, sailboards or similar aquatic boards, referred to generically herein as xe2x80x9cboardxe2x80x9d or xe2x80x9cboards.xe2x80x9d
2. Description of the Related Art
Surfboards and sailboards are of similar shape, however the sailboard is generally manufactured in a mold, while the surfboard is fabricated using a labor-intensive moldless or custom method of construction. The conventional molds used in surfboard and sailboard construction comprise top and bottom halves that meet at the perimeter and thereby delimit an internal cavity; the concave, female surface of the mold defines the board""s exterior shape, and imparts a smooth surface to the exterior skin. Currently available molded production techniques restrict the shape of the board to an exact duplicate, which generally limits molded production to the less demanding design of the sailboard. For molded surfboard production, the wide variation in size and shape requires the manufacturer to invest in a large and prohibitively expensive inventory of molds, and eliminates the many custom design modifications that are made in the prior art as a matter of routine.
The surfboard is typically constructed without a mold. The board is individually hand-shaped from a polyurethane foam blank, and the fiberglass and resin are applied by hand over the shaped foam core. The process is labor-intensive, requires considerable skill, and involves structural problems that dictate dividing the production process into two separate steps, with the foam blank supplied by a separate manufacturer.
To enhance the strength of the foam, the blank is molded in an extremely strong, heavy mold made of reinforced concrete. This allows an excess of liquid pre-foam to be poured in the mold; as the foam expands, the excess compresses under high pressure against the surface of the mold and produces a density-gradient in the blankxe2x80x94the foam is soft and weak in the center and becomes progressively harder and denser towards the surface. To avoid removing too much of the harder, denser surface foam during shaping, the blank is molded close-to-shape, or as thin as possible. This close-to-shape molding has the drawback of increasing the requisite number of blank molds for surfboard production, and frequently leaves insufficient foam in the nose and tail areas of the blank for the shaper to produce the desired lengthwise bottom curvature or rocker in the board.
The molded-in rocker of the blank must therefore be modified by the blank manufacturer by gluing the blank to a wooden center spar or stringer cut to dimensions specified by the customer, and usually selected from a list of stock lengthwise rocker modifications. Clark Foam of Laguna Niguel, Calif., (www.clarkfoam.com) lists in its Rocker Catalog the dimensions of over two thousand different templates available to modify the molded-in rocker curvature produced by the more than sixty blank molds offered for surfboard production. Molding the density-gradient into the foam and providing the frequent lengthwise rocker modifications are expensive but essential, because the board""s ability to withstand impact and bending loads is very low.
The single fiberglass ply used on the bottom of the board will usually dent or fracture with moderate finger/thumbnail pressure, while the double or triple layer used to reinforce the deck (or top surface of the board) in the tail area where the rider stands often fatigues, becomes permeable to water, then fails and completely delaminates under the repeated high pressure of the rider turning the board. Shaping also limits the effectiveness of the longitudinal reinforcementxe2x80x94it makes wood the material of choice for the center spar and also makes it impractical to ad top and bottom spar caps (i.e. the top and bottom reinforcing flanges in an I-beam)xe2x80x94the lack of effective longitudinal reinforcement leaves thinner surfboards in particular susceptible to breakage. In custom-board production, a basic problem is the one-to-one weight ratio of skin material to interior core. Currently, enhancing the strength-to-weight ratio entails the high costs and lengthy mold cycle of a fiber-reinforced structural sandwich skin, in the more expensive of the two basic methods of molded manufacture outlined briefly below.
The rapid mold-cycle and inexpensive thermoplastic skin of a blow-molded, rotationally-molded, or vacuum-formed board generally offers lowest costs of production. The specifications of U.S. Pat. No. 5,094,607 to Masters and U.S. Pat. No. 4,065,337 to Alter et. al, which describe rotational and vacuum thermoforming methods applicable to surfboards, sailboards and other small watercraft, are incorporated herein. U.S. Pat. No. 4,713,032 to Frank, the specification of which is incorporated herein, is directed to low-cost methods in which a fiber-reinforced resin foams to fill the void between a pre-molded EPS core and the surface of the closed mold. Using quick-setting, foamed polyurethane resin in the skin, the cited invention achieves a rapid mold-cycle of about twenty minutes per board and high production from the molding tool of as many as twenty-four boards per day.
In the above methods, the strength of the fiber reinforcement is greatly reduced by the foaming of the resin matrix, or is absent altogether. Using a rotational mold, three separate charges of resin, the second of which foams, are often used to create a thicker, stronger skin xe2x80x9csandwich skin;xe2x80x9d similarly, a thin sheet of PVC foam is often used as a sandwiched core between the layers of laminate to create a fiber-reinforced, foamed plastic sandwich skin.
Due to the inherent weakness of the above materials, strength-to-weight and skin-to-interior core ratios fall well below expensive, high-performance sailboards, that eliminate the blowing agent in the fiber-resin to create a much higher strength xe2x80x9cstructural sandwichxe2x80x9d skin. The structural sandwich is expensive to fabricate because of the very long mold cyclexe2x80x94vacuum pressure is used to eliminate entrapped air and voids and causes the sandwich core/laminate to conform to the shape of the mold; to prevent the spring-back of the sandwich core the material remains in the mold under vacuum pressure for about two to three hours, until the resin has completely cured. The shape of the opened mold creates an additional problemxe2x80x94the sharp, concave edge contours tend to create a dam, and the sandwich core layer, by blunting the effectiveness of the squeegee in removing excess resin from the laminate, prevents the skin from attaining optimum strength and lighter weight.
In the interior core, EPS (expanded polystyrene) bead foam requires separate pre-molding in a steam chest, but is preferred over polyurethane foam due to its lighter weight-containing the expansion of liquid polyurethane pre-foam injected into the mold""s interior generally requires an extremely strong mold, steel reinforcing jigs and a hydraulic press to prevent mold distortion or buckling under the high pressure. In prior art described in U.S. Pat. No. 5,023,042 to Efferding, the wet epoxy laminate/PVC sheet foam of the structural sandwich skin fits into molded-in recesses in the EPS core and the entire assembly is placed in the mold, the exterior of which precludes resin removal by hand. Vacuum is applied to press the components tightly together and squeeze excess resin out in the process, but the pressure is limited to about 12-15 inches of Hg to prevent the mold from distorting and the foam core collapsing. Full vacuum (27 in. Hg) may be applied using the evenly flexing upper mold half disclosed in the invention to Efferding, which eliminates distortion problems by compressing the EPS interior core evenly, creating a permanent compression set of about three sixteenths of an inch in the finished board. Internal shear webs, spars, etc. become problematic, however, as they tend to cause distortion problems to reappear under vacuum.
The high-strength obtained with expensive, thermo-setting epoxy xe2x80x9cprepregxe2x80x9d/honeycomb skin-core combinations as described in U.S. Pat. No. 4,964,825 to Paccoret, et. al and U.S. Pat. No. 5,266,249 to Grimes III, et. al, the specifications of which are incorporated herein, allows the interior of the board to left largely hollow, with a longitudinal shear web/transverse bulkhead structure serving as support. Manufacture entails high material cost, a long mold cycle at high temperature, and often a high-pressure autoclave cure.
Undesirable flexural characteristics have relegated the use of resilient foams to beginner and rental boards; due in part to high production costs, boards made with a sufficiently stiff interior structure as described in U.S. Pat. No. 3,543,315 to Hoffman and U.S. Pat. No. 5,489,228 to Richardson, et. al, the specifications of which are incorporated herein, have heretofore comprised an insignificant portion of the overall market.
At the time of the present invention, the board-making arts had need of a method of high-strength board fabrication with a reduced mold-cycle to make production costs competitive with low-cost thermoplastic and fiber-reinforced foamed plastic methods outlined above. This invention allows high-strength fiber-reinforced plastic to be combined with rapidly formed thermoplastic in the skin, uses optional resilient material to absorb impact and bending loads and, by incorporating principles during manufacture that allow alterations in shape, permits the molded production of custom-shaped boards.
Embodiments of the present invention allow opposing sides of the male or female surface of a single shape-defining board mold, whether divided into top and bottom, right and left halves, or of substantially one piece construction, to produce the plurality of different board configurations necessary in the molded production of custom shaped boards. Further, because the shape of the material itself may be modified after removal from the mold, a simply constructed mold made according to the present invention may define the shape of the material in such a way that substantial modifications are possible after the shape is initially defined, so that a variety of individual flotation, planing area and performance requirements may be accommodated.
For example, in an embodiment of the present invention, vacuum thermoforming techniques may be used to mold a layer of thermoplastic material, such as a sheet of high-density plastic foam, to create a thin, arcuate foam shell in the shape of one right- or left-hand side of the board. During subsequent steps of production, as it receives a fiber-reinforced plastic skin and foam for the interior core, its width may be altered according to where excess material is trimmed to create a longitudinal centerline for the board, the tail made wider relative to the nose and vise versa, and the volume of the board may be modified according to the thickness of material used in the interior core.
Further, during molding, the thin layer of exterior skin material may be of sufficient thickness to bridge small gaps and mask minor imperfections on the surface of the mold, allowing the shape-defining mold to be divided into separate parts designed to be moved, then fixed and set so as to change dimensions, describe different curves and modify various parameters of the board""s design. In the present invention, for example, the bottom panel of the mold may be designed to bend lengthwise to alter the rocker curvature of the board, the deck panel made adjustable to control thickness, a flexible rail component may be made to modify the board""s outline and width; added rail segments and/or adjustable nose and nose and tail components then allow changes in length at either end. Reference for the movement and fixed attachment of the mold parts may be provided an external structure, such as a mold base, which may be placed parallel to the mold""s longitudinal axis of symmetry, and/or each other.
When fixed attachment of the shape-defining subparts is to a mold base, the exterior or male surface of the mold may be used, and the mold thus configured and can accommodate virtually all the common modifications required within a particular style of board. The added compound curvature of certain design features, however, can limit the bending capacity of the affected mold panel or rail component sufficiently to make additional bending difficult if not impossible. To accommodate these design features, the mold components may be reversed and attached to an external frame, thereby creating the concave cavity of a female mold. After the rocker, thickness and various design parameters of the mold are set, foam may be molded in the cavity to produce a foam blank that, upon removal, can quickly have the desired features shaped into the foam by hand; the shaped blank then provides the (male) mold needed to form surface layer(s) that comprise the board""s exterior skin. The male/female mold configurations thus allow the production of custom designs; further, the method of manufacture reduces the mold cycle of high-strength board fabrication.
For example, because the shape of the board may be defined by a layer of rapidly formed thermoplastic foam, it is also possible to vacuum thermoform an additional thin, inexpensive sheet of polycarbonate, acrylic, polypropylene etc. that serves as a mold to impart a smooth surface in a fiber-reinforced plastic skin. Combined, the two surfaces have sufficient stability for the laminated skin/female mold assembly to be removed from the expensive shape-defining mold before the resin has fully hardened, thus reducing the mold-cycle (of the shape-defining mold) to the time needed to initially pre-mold the thermoplastic material and apply the laminate, under ten minutes per side in each operation.
Structurally, molding the board in right and left halves produces a stronger, seamless monocoque rail, and allows the bond-line and its attendant reinforcement to moved away from the perimeter and placed along the longitudinal centerline of the board, where the same weight of material may be used to create a high strength composite spar that guards against board breakage. The laminate may be applied with the width of the board at right angles to the worktable, where gravity provides an effective aid in removing excess resin. The thin, flexible female surface allows substantial squeegee pressure to pass through to the laminatexe2x80x94unobstructed, the resin quickly runs off the smooth, vertical sides of the molded foam shell, leaving an absolute minimum within the fiber. The laminate""s enhanced tensile, compressive, and flexural strength in bending may then be complemented by incorporating resilient foam into the interior core and skin, to allow the board to absorb even greater impact and bending loads without damage.
Other advantages include a more efficient use of spacexe2x80x94the board may be positioned so that its thickness, rather than its width, occupies manufacturing area during construction and throughout the cure; this feature also makes it possible to realize major labor savings by using a mechanical fabric-impregnator to quickly pre-saturate the fiberglass cloth. It will be seen that the principles disclosed herein may be applied to a variety of manufacturing techniques and mold configurations. For example, the board mold may have a single continuous shape-defining surface, be divided into top and bottom as well as right and left halves, and incorporate male/female shape defining combinations as well as reversible male/female surfaces. It will be seen that each of these mold configurations may have particular advantages according to specific board design and manufacturing requirements, which will be more fully explained and better understood given the context provided by the detailed description of the invention, and upon viewing the drawings.